1. Field of the Invention
The present invention relates to an antifungal agent for the prevention and treatment of aquatic fungal infections comprising the essential oil of sweet flag, which is a natural plant extract developed to replace existing chemical agents such as malachite green or antibiotics used for the prevention and treatment of aquatic fungal infections in aquaculture. More particularly, the present invention relates to an antifungal agent having a superior effect for the prevention and treatment of aquatic fungal infections when compared with malachite green, which is known as carcinogen and banned from use.
2. Description of the Related Art
In general, the fertilization of eggs in aquaculture refers to the mass production of fertilized eggs under human control in a restricted area. It is a stage prior to the production of larval fish. Aquatic fungal infections have been known since long ago. Although healthy fish are seldom infected, water moulds proliferate on the dead cells at the inflammation or wound of unhealthy fish like fluffs. Such aquatic fungal infection is caused by the proliferation of the phycomycete Saprolegnia parasitica at the wound. The infection prevails in spring when the water temperature becomes 14° C. or higher. It persists through the year excluding the high water temperature period. It disappears when the water temperature increases over 20° C. The infection is caused by the parasitization of water moulds at the wounds formed during the transfer of fish, selection, egg collection, sperm harvesting, etc., parasitizations by skin flukes (Gyrodactylus), lernea, etc., inflammations caused by such pathogenic bacteria as Aeromonas hydrophila, inflammations caused by nutritional diseases or abnormal body surfaces caused by bad health. Typically, it invades the epithelial tissue and proliferates hypha, causing the fish to die. Also, it causes the loss of appetite and lets the fish break away from the group. The water moulds proliferating in dead fish eggs surround the living eggs and suffocate them.
Until recently, various antibiotics and chemical agents like malachite green have been used improperly in order to remove the water moulds that parasitize fish or fertilized eggs and cause them to perish. Among them, malachite green (C23H25ClN2) is a light bluish-green, triphenylmethane-based basic dye usually used for the staining of fiber, wood, paper, straw and other materials. It has also been used as reagent or indicator in analytical chemistry. Also, it has been used as topical antiseptic in the field of medicine. Particularly, it has been used to prevent infections by fungi or bacteria during sterilization of fertilized eggs, culturing, transfer and storing in aquaculture since it is effective against fungi and Gram-positive bacteria. However, suspected as a carcinogen, its use is banned in many countries.
Antimould agents and antifungal agents are used to treat fungi. These agents are classified into the following two groups: (1) those that chemically affect the cell wall or cell membrane of fungi and interrupt the normal enzymatic functions of the cells; and (2) those that penetrate the cell wall or cell membrane and inhibit the enzymatic actions including nucleic acid and protein synthesis. Industrially, the group (1) antimould agents that disturb the cell wall or cell membrane are used in general. Antifungal agents are agents for controlling pathogenic fungi. Use of the agents has increased with the abrupt increase of fungal infections. A lot of pesticides are being developed in the phytopathological field to destroy pathogenic moulds harmful to the crops. At present, copper compounds and dithiocarbamate compounds are used worldwide. In addition, formaldehyde, copper sulfate, methylene blue, bithionol, oxolinic acid, potassium permanganate, calcium hypochlorite, calcium hydroxide, antibiotics (chloramphenicol, oxytetracycline, chlortetracycline), sulfa drugs (sulfamerazine, sulfamonomethoxine, sulfadimethoxine sodium), and so forth are currently used in the aquaculture industry to reduce the damage caused by fungi. But, as suggested by many researches, these substances may be very harmful to both human body and environment. Accordingly, researches are being carried out on various physiologically active materials and antifungal substances existing in the nature.